NEW YORK — With masks, ventilators and political goodwill in desperately short supply, more than one-fifth of the world’s population was ordered or urged to stay in their homes Monday at the start of what could be a pivotal week in the battle to contain the coronavirus in the U.S. and Europe.

Partisan divisions stalled efforts to pass a colossal aid package in Congress, and stocks fell again on Wall Street even after the Federal Reserve said it will lend to small and large businesses and local governments to help them through the crisis.

Warning that the outbreak is accelerating, the head of the World Health Organization called on countries to take strong, coordinated action.

“We are not helpless bystanders,” Tedros Adhanom Ghebreyesus said, noting that it took 67 days to reach 100,000 cases worldwide but just four days to go from 200,000 to 300,000. “We can change the trajectory of this pandemic.”

Britain became the latest European country to order a near lockdown, imposing its most draconian peacetime restrictions.

The scramble to marshal public health and political resources intensified in New York, where a statewide lockdown took effect amid worries the city of 8.4 million is becoming one of the world's biggest hot spots. More than 12,000 people have tested positive in the city and almost 100 have died.

The governor announced plans to convert a mammoth New York City convention center into a hospital with 1,000 beds. The mayor warned that the city's hospitals are just 10 days away from shortages in basic supplies.

“This is going to get much worse before it gets better. We are still in the relative calm before the storm,” Gov. Andrew Cuomo said at the Jacob K. Javits Convention Center.

In Italy, the hardest-hit country, declines in both new cases and deaths for a second consecutive day provided a faint glimmer of hope, though it is too soon to say whether the crisis is leveling off.

Italian officials said Monday that the virus had claimed just over 600 more lives, down from 793 two days earlier. All told, the outbreak has killed more than 6,000 Italians, the highest death toll of any country, and pushed the health system to the breaking point there and in Spain.

The risk to doctors, nurses and others on the front lines has become plain: Italy has seen at least 18 doctors with coronavirus die. Spain reported that more than 3,900 health care workers have become infected, accounting for roughly 12 percent of the country's total cases.

British health workers pleaded for more gear, saying they felt like “cannon fodder.” In France, doctors scrounged masks from construction workers, factory floors, an architect.

“There's a wild race to get surgical masks,” François Blanchecott, a biologist on the front lines of testing, told France Inter radio. “We're asking mayors' offices, industries, any enterprises that might have a store of masks.”

The way U.S. officials respond to the severe pressure on hospitals — and people's willingness to keep their distance from others — will prove critical in coming days, public health experts said.

“Actions taken right now will have a huge impact on the course of this epidemic in the U.S.,” said Josh Michaud, associate director of global health policy with the Kaiser Family Foundation in Washington. “It’s an important moment."

President Donald Trump told reporters he believes the U.S. economy, which has been virtually shut down, could be reopened in weeks, not months. Trump wouldn't say when businesses would be up and running but that he wasn't “looking at months, I can tell you right now. We're going to be opening up the country.”

Amid complaints of hospitals running low on masks, gloves and other critical gear, Trump signed an executive order making it a crime to stockpile supplies needed by medical workers. Attorney General William Barr said investigators will go after those hoarding goods on “an industrial scale” and price gouging.

“If you are sitting on a warehouse with surgical masks, you will be hearing a knock on your door,” Barr told reporters.

China is now sending planeloads of protective gear and doctors to Europe as the crisis kept easing in the country where the virus first emerged late last year. For more than a week, the vast majority of China’s cases have been in people coming into the country rather than from community spread, according to the National Health Commission.

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“The U.S. is completely wasting the precious time that China has won for the world,” said Geng Shuang, the Chinese Foreign Ministry spokesman.

Dr. Anthony Fauci, the U.S. government's top infectious-disease expert, promised that medical supplies are about to start pouring in and will be “clearly directed to those hot spots that need it most.”

Democratic presidential candidate Joe Biden criticized Trump for not using the full force of federal authority to combat the virus.

On Capitol Hill, a nearly $2 trillion plan that would prop up businesses and send checks to American households has stalled. Democrats argued it was tilted toward corporations rather than workers and health care providers.

Meanwhile, industries big and small continued to shut down. Boeing announced it was suspending production in the Seattle area, where it has two mammoth aircraft plants employing about 42,000 people.

More than 375,000 people worldwide have been infected and over 16,000 have died from the virus, according to a running tally kept by Johns Hopkins University. More than 1.5 billion people around the globe have been instructed to stay in their homes.

British Prime Minister Boris Johnson added to those orders Monday and directed shops that don't sell essential goods to shut down. He warned that police would be authorized to break up public gatherings of more than two people. Johnson faced pressure for tougher measures because many have ignored advice on social distancing.

After just a few weeks, the U.S. has more than 43,000 cases and more than 500 deaths. Indiana, Michigan and West Virginia joined states including California, Illinois and New York in asking or ordering residents to stay home and keep businesses closed — directives that cover more than one-third of the U.S. population in a patchwork of rules imposed by governors or cities.

Former Hollywood studio boss Harvey Weinstein tested positive at the prison in New York where he is serving a 23-year sentence for rape and sexual assault, the head of the guards union said.

For most people, the coronavirus causes only mild or moderate symptoms, such as fever or coughing. But for some older adults and people with existing health problems, it can cause more severe illness, including pneumonia. Over 100,000 people have recovered, mostly in China.

Authorities kept up their push to get people to stay home, but some were not listening. Social media showed snapshots of packed London Underground trains.

In New York, Cuomo fumed over gatherings of young people in violation of his order that everyone stay 6 feet (2 meters) apart, saying, "It’s reckless and it's violative of your civic spirit and duty as a citizen, as far as I’m concerned.”

In a city where many people live in buildings with small elevators, a 21-story high-rise in the Chelsea neighborhood posted a notice in the lobby warning that there should be just one person per elevator, and those going to the laundry room shouldn't use a washing machine next to another one in use.

“People are really only going to get food and going back. That’s what we need,” said Matt Comet, making a brief dash into the nearly empty streets of his Manhattan neighborhood to pick up a carryout meal.

“I’m OK to have a book and watch TV for a bit, but if it continues for another month, another two months, it’ll be pretty crazy,” he said.

India took the extraordinary step of shutting down the nation's vast rail system, the lifeblood of the country of 1.3 billion people.

Japanese Prime Minister Shinzo Abe acknowledged that postponing this year's Summer Olympics in Tokyo could be unavoidable. The International Olympic Committee said it will examine the situation over the next few weeks.

U.N. Secretary-General Antonio Guterres called for an immediate cease-fire in conflicts around the world to tackle the pandemic.

“It is time to put armed conflict on lockdown and focus together on the true fight of our lives,” he said.